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Biphasic effect of phorbol myristate acetate on histamine secretion induced by compound 48/80 in rat peritoneal mast
Abstract:
Rat peritoneal mast cells which had been preincubated with phorbol myristate acetate (PMA, 100 ng/ml) for 30 sec elicited an enhanced histamine secretion induced by a potent secretagogue, compound 48/80. But a longer (5 min) preincubation with PMA followed by the agonist-stimulation induced a suppressed histamine secretion. A 5 min-PMA-pretreatment inhibited the compound 48/80-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) in [32P]-labeled cells. PMA-treatment alone for 5 min induced an activation of Ca2+-efflux monitored by 45Ca2+. The inhibition of histamine secretion induced by a 5 min-PMA-pretreatment followed by the agonist-stimulation may partly be attributed to the decreased intracellular Ca2+ concentration, [Ca2+]i, probably due to the depressed PIP2 breakdown and enhanced Ca2+-efflux. On the other hand, a 30 sec-preincubation with PMA followed by compound 48/80-stimulation induced a slight but significant increase in histamine secretion. In this case, neither breakdown of PIP2 nor Ca2+-influx was enhanced to raise the [Ca2+]i. Although we are unable to explain the mechanism for the enhancement of histamine secretion by a short (30 sec) PMA-preincubation, these results suggest that the biphasic effects of PMA on histamine secretion are mediated by intracellular Ca2+ mobilization probably via protein kinase C activation.
Insights
Phorbol myristate acetate (PMA) has biphasic effects on rat mast cell histamine secretion. Short PMA exposure enhances secretion, while longer exposure suppresses it, likely via protein kinase C-mediated calcium signaling.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Mast cells play a crucial role in allergic responses and inflammation.
- Histamine secretion from mast cells is a key mediator of these processes.
- Phorbol myristate acetate (PMA) is a potent activator of protein kinase C (PKC).
Purpose of the Study:
- To investigate the biphasic effects of PMA preincubation on histamine secretion from rat peritoneal mast cells.
- To elucidate the role of intracellular calcium (Ca2+) mobilization and phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis in PMA-modulated histamine release.
Main Methods:
- Rat peritoneal mast cells were preincubated with PMA (100 ng/ml) for varying durations (30 sec and 5 min).
- Histamine secretion was induced using the secretagogue compound 48/80.
- Phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis was measured in [32P]-labeled cells.
- Calcium efflux was monitored using 45Ca2+.
Main Results:
- A 30-second PMA preincubation enhanced compound 48/80-induced histamine secretion.
- A 5-minute PMA preincubation suppressed compound 48/80-induced histamine secretion.
- The 5-minute PMA pretreatment inhibited PIP2 hydrolysis and enhanced Ca2+-efflux, leading to decreased intracellular Ca2+ concentration ([Ca2+]i).
Conclusions:
- PMA exhibits dose- and time-dependent biphasic effects on mast cell histamine secretion.
- These effects are likely mediated by protein kinase C (PKC) activation and subsequent modulation of intracellular calcium mobilization.
- Short PMA exposure may prime mast cells for enhanced secretion, while prolonged exposure desensitizes them through altered calcium handling.